The blockage or mechanical failure of a reverse osmosis (RO) or nanofiltration (NF) membrane element can lead to significant downtime of a membrane based water purification plant. There are several offline optical and acoustical devices and methods used to identify a membrane element mechanical failure or the amount of membrane element blockage. However, these devices and methods cannot provide online monitoring and are expensive and time consuming. Accordingly, there is a need for a membrane element mechanical failure and blockage sensor system to identify the presence of a mechanical failure and the presence and amount of blockage in a membrane element. Further, there is a need for a method of using the sensor system to help ensure timely cleaning and/or replacement of the mechanically failed and/or blocked membrane elements.